The invention is in the field of electronic reproduction technology and is directed to a method for engraving printing cylinders in an electronic engraving machine, to an engraving stylus monitoring device for an electronic engraving machine, and is also directed to an electronic engraving machine having such an engraving stylus monitoring device.
DE-C-2508734 already discloses an electronic engraving machine for engraving printing cylinders with an engraving element. The engraving element having an engraving stylus controlled by an engraving control signal as a cutting tool moves in an axial direction along a rotating printing cylinder. The engraving stylus cuts a sequence of cups arranged in a printing raster into the generated surface cylinder. The engraving control signal is formed by a superimposition of a periodic raster signal for generating the printing raster with image signal values that define the tonal values to be reproduced between “black” and “white”. Whereas the raster signal effects an oscillating lifting motion of the engraving stylus for engraving the cups arranged in the printing raster, the image signal values determine the cut depths of the engraved cups corresponding to the tonal values to be reproduced.
DE-A-23 36 089 discloses an engraving element that essentially comprises a rotatory system and an electromagnetic drive for the rotatory system. The rotatory system comprises a shaft, an armature, a bearing for the shaft, a restoring element and a damping mechanism. A lever-shaped stylus holder is attached to the shaft, this carrying the engraving stylus. The electromagnetic drive for the rotatory system comprises an excitation coil charged with the engraving control signal and a stationary electromagnet in whose air gap the armature of the rotatory system moves. The drive effects a rotatory motion of the shaft oscillating by small angles, and the stylus holder together with the engraving stylus implements a corresponding, oscillating lifting motion in the direction of the generated surface of the printing cylinder for engraving the cups.
In practice, it occasionally occurs that the engraving stylus is damaged during the engraving of a printing cylinder, for example due to wear or due to mechanical overloading, or even break offs. In this case, the partially engraved printing cylinder is unuseable as a printing form and a new printing cylinder must be engraved. Damage to or breakage of the engraving stylus thus disadvantageously causes a loss of time in printing form manufacture that, in particular, can be substantial when engraving printing cylinders for packaging printing or decorative printing since the engraving of such printing cylinders can last several hours.
WO-A-9951438 already discloses an engraving machine for engraving printing cylinders wherein the actual dimensions of cups engraved on the printing cylinder are determined for recognizing damage to the engraving stylus, and error values are determined by comparing the actual dimensions to rated dimensions and wherein a signal for aborting the engraving is generated when the identified error values respectively exceed a prescribed limit value of tolerance range